detail

1630s, from French détailler "cut up in pieces; narrate in particulars," from Old French detaillier, from detail (see detail (n.)). Related: Detailed; detailing.

detail

n.

c.1600, from French détail, from Old French detail "small piece or quantity," literally "a cutting in pieces," from detaillier "cut in pieces," from de- "entirely" (see de-) + taillier "to cut in pieces" (see tailor).

Modern sense is from French en détail "piece by piece, item by item" (as opposed to en gros), a commercial term used where we would today use retail. Military sense is 1708, from notion of "distribution in detail of the daily orders first given in general," including assignment of specific duties.

in detail

With close attention to particulars; thoroughly. For example, She explained her theory in detail. It is also put asgo into detail, meaning “to investigate thoroughly,” as in You know what I mean, so I needn't go into detail. The first expression dates from about 1600, the second from the late 1800s.